Ammonia is also sensitive to gravity,
but unlike methane and CO, ammonia is insensitive to mixing, which makes it a proxy for gravity.
We did not explore temperatures low enough to determine the transition from N\(_2\)  to ammonia
in planets, but it is nearly as abundant as N\(_2\) 
at 500 K in brown dwarfs, which is broadly consistent with the
observed properties of the Y dwarfs [1]} for which \(\rm NH_3\)  is seen in H band.
On the other hand, ammonia persists as an abundant minor species to rather high temperatures
and this is
consistent with it being readily detected in mid-IR spectra of T-dwarfs [2]}.
HCN might become interesting in high gravity brown dwarfs if vertical mixing is very vigorous.
